Many manufacturers buy cars from other makers to benchmark while they are developing a new vehicle. Honda was no different when it was developing the Ohio-built Acura NSX. One of its purchases was the highly regarded Porsche 911 GT3, bought to assess its steering, vehicle dynamics project leader Nick Robinson told Automotive News.

Usually, makers go to dealerships just like regular customers, and the rival carmaker is none the wiser. Except these days, with ever more information being stored in the vehicle's black box, a rogue customer is easier to spot.

Porsche realized that this particular customer was Honda's NSX development team after the GT3 was recalled to fix an issue with the engine connecting rods. When the car was returned, Robinson remembers, the team found a message written under the engine cover: "Good luck Honda from Porsche. See you on the other side."

To develop the $157,800 hybrid, the Honda team also bought a McLaren 12C. The car needed to return to the dealership a few times for remedial work, but McLaren didn't quite catch on.

Said Robinson: "They wanted to know, where did you go 205 mph? What track?"